1) Field of the Invention
The present invention relates to an optical module that comprises an optical element and a thermoelectric semiconductor.
2) Description of the Related Art
The Internet has become popular. As a result, there is an increasing demand for large-capacity data transmission. For the large-capacity data transmission, it is necessary to have an optical system that can transmit optical signals via an optical fiber faster.
A laser diode is used as a light source in the optical system. An optical module transmits the light generated by the laser diode to the optical fiber.
In order to increase the transmission speed of optical signals, it is necessary to execute at high speed the intensity modulation of the light generated by the laser diode. It is also necessary to improve the performance of the optical module.
Optical modules that transmit optical signals at a high-speed bit rate of 2.5 Gb/s have been put into practical use. Moreover, development of optical modules that transmit optical signals at still higher speed of 10 Gb/s have been progressed.
In order to realize large-capacity optical communications, it is necessary to provide a high-density optical fiber network by using an optical module that can transmit optical signals at a high-speed bit rate. For this purpose, a stable supply of low-cost optical modules has been desired.
FIGS. 9A and 9B show structures of a conventional optical module disclosed in Japanese Patent Application Laid-Open No. H11-121862. FIG. 9A shows a top plan view of the conventional optical module in a state that an upper lid is dismounted. FIG. 9B shows a side view of this optical module cut along a line Axe2x80x94A.
In FIGS. 9A and 9B, a reference number 1 denotes a laser diode that converts an electric signal into an optical signal, 2 denotes a mount on which the laser diode 1 is mounted, and 3 denotes a carrier on the upper surface of which the mount 2 is installed. A reference number 4 denotes a package that accommodates the carrier 3 and seals the laser diode 1, and 5 denotes a thermistor that is provided on the upper surface of the carrier 3. A reference number 6 denotes a thermo-module that heats or cools the laser diode 1 to avoid a fluctuations in the temperature of the laser diode 1 due to the heating of the laser diode 1 by itself or the heat from the outside of the package 4. Such heating or cooling of the laser diode 1 is performed to stabilize the characteristic of the laser diode 1. A reference number 7 denotes a terminal that transmits signals between the carrier 3 and the outside of the package 4. The elements 1 to 7 constitute an optical module 8.
An automatic temperature control (ATC) circuit 9 is provided outside of the package 4.
To execute intensity modulation of optical signals, a bias current Ib and a modulation current Im is applied to the laser diode 1. When there is a rise in the temperature of the laser diode 1, the light output of the laser diode 1 decreases, or the oscillation stops. When there is a fall in the temperature of the laser diode 1, the light output increases. The temperature of the laser diode 1 rises even as a result of self-heating.
The ATC circuit 9 inputs-outputs control signals to/from the optical module 8 via the terminal 7. The ATC circuit 9 receives information from the thermistor 5, which detects the temperature of the laser diode 1, about the temperature of the laser diode 1, and adjusts a driving current Is supplied to the thermo-module 6 based on the temperature of the laser diode 1 so that the laser diode 1 is always kept at a constant temperature. Since the temperature of the laser diode 1 is always constant, a stable optical output can always be obtained from the laser diode 1.
The thermo-module 6 is usually constructed of about 12 to 40 thermoelectric semiconductors. Each thermoelectric semiconductor consists of an N-type semiconductor 10a and a P-type semiconductor 10b. The thermoelectric semiconductors are arranged parallel to each other. The thermoelectric semiconductors conduct heat in a direction (heat transmission direction) that is parallel to the long side of the paper on which the FIG. 9B has been drawn. Each thermoelectric semiconductor is connected to a dielectric substrate at each end of the thermoelectric semiconductor in the heat transmission direction. For example, dielectric substrate 11a is connected to one end and dielectric substrate 11b is connected to the other end of the N-type semiconductor 10a. Wiring patterns are prepared in the dielectric substrates. The dielectric substrates of one thermoelectric semiconductor are electrically connected to the dielectric substrates of adjoining thermoelectric semiconductor such that all the thermoelectric semiconductors are connected in series.
The thermoelectric semiconductors operate according to the Peltier effect. Whether to perform heating or cooling, can be decided by simply changing the direction of the current supplied to the thermoelectric semiconductors. Therefore, the thermoelectric semiconductors are suitable for the temperature control of the laser diode 1.
In the conventional optical module, the thermo-module 6 is mounted on the base of the package 4, and the carrier 3 is mounted on the thermo-module 6, so that the heat transmission direction of the thermoelectric semiconductors becomes parallel to the height direction of the thermoelectric semiconductor. However, because the thermo-module 6 is mounted on the base, and the carrier 3 is mounted on the thermo-module 6, there has been a problem that the height of the optical module increases. Consequently, the package becomes large, and this has been a barrier for the cost reduction of the optical module.
Moreover, since a large number of the thermoelectric semiconductors are used, the workload on the thermo-module 6 increases, and the total power consumption increases. Further, the assembling becomes complex and takes time. In addition, the ATC circuit 9, which is expensive, has to be provided. These factors have also interrupted the cost reduction of the optical module.
Optical modules that do not have the above mentioned problems have been developed and appeared in the market. These optical modules use a mini dual in-line (mini-DIL) type package. Moreover, these optical modules do not have a thermo-module. Therefore, it is possible to decrease the height of the optical module, and realize low cost.
However, in order to output a stable optical signal at the transmission speed of the order of 10 Gb/s or more, it is necessary to minimize the operation temperature of the laser diode. Concretely, it is necessary to set the operation temperature of the laser diode to about 70xc2x0 C. or below. However, there is a demand that the optical module even functions at the environmental temperature of about 70xc2x0 C. If the environmental temperature is 70xc2x0 C., the temperature of the laser diode becomes higher and exceeds the operation temperature of the laser diode due to self-heating. Consequently, it is not possible to stably operate the laser diode if the environmental temperature is 70xc2x0 C. or higher.
Therefore, there have been problems that, if the environmental temperature is 70xc2x0 C. or higher, then either that laser diode does not exhibit desired characteristics or a provision has to be made to cool the surrounding of the laser diode so that the environmental temperature falls to 65xc2x0 C. or below.
Various technical developments have been carried out so far to expand the range of operation temperature of the laser diode. However, expansion of the operation temperature of the laser diode has always been a difficult task.
To conclude, the conventional optical modules have a problem that the overall height is tall and cost reduction is not possible. Moreover, the optical modules that use the mini dual in-line (mini-DIL) type package and do not have a thermo-module have a problem that the temperature control of the laser diode is not possible (because there is no thermo-module).
It is an object of this invention to provide a low-cost and small optical module and that can achieve a high-speed operation even at a high temperature.
The optical module according to one aspect of the present invention has a substrate and an optical element is mounted on the surface of this substrate. Moreover, there is a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel, the thermoelectric semiconductor having two ends, a heat radiation side, and a heat absorbing side. This thermoelectric semiconductor is arranged such that at least one end of the thermoelectric semiconductor is mounted on the surface of the substrate, and a direction from the heat absorbing side to the heat radiation side is parallel with the substrate. As referred to herein the words xe2x80x9cradiatexe2x80x9d or xe2x80x9cradiationxe2x80x9d are used in a generic sense to refer to the transfer or giving off of heat, rather than to any specific means of transferring or giving off heat such as electromagnetic radiation.
The optical module according to another aspect of the present invention has an optical element and a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel. The P-type semiconductor and the N-type semiconductor have two ends. Moreover, there is a first substrate having at least front and rear surfaces. The optical element is mounted on the front surface on the first substrate, and a side surface of one end of the P-type semiconductor and a side surface of one end of the N-type semiconductor are connected to the front surface of the first substrate. Moreover, there is a second substrate that is disposed with a distance from the first substrate. The second substrate has at least front and rear surfaces. A side surface of the other end of the P-type semiconductor and a side surface of the other end of the N-type semiconductor are connected to the front surface of the second substrate. Moreover, there is a base on which the rear surfaces of the first and second substrates are mounted.
The optical module according to still another aspect of the present invention has an optical element and a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel. The P-type semiconductor and the N-type semiconductor have two ends. Moreover, there is a first substrate having at least front and rear surfaces. The optical element is mounted on the front surface on the first substrate, and a side surface of one end of the P-type semiconductor and a side surface of one end of the N-type semiconductor are connected to the front surface of the first substrate. Moreover, there is a second substrate that is disposed with a distance from the first substrate. The second substrate has at least front and rear surfaces. A side surface of the other end of the P-type semiconductor and a side surface of the other end of the N-type semiconductor are connected to the front surface of the second substrate. Moreover, there is a case on which the rear surfaces of the first and second substrates are mounted.
The optical module according to still another aspect of the present invention has an optical element and a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel. The P-type semiconductor and the N-type semiconductor have two ends. Moreover, there is a substrate having at least one surface. The optical element is mounted on the surface of the substrate. A side surface of one end of the P-type semiconductor and a side surface of one end of the N-type semiconductor are connected to the surface of the substrate. Moreover, there is a case that houses the substrate and that has a side wall. The side wall has a surface that is disposed at a distance from the substrate. A side surface of the other end of the P-type semiconductor and a side surface of the other end of the N-type semiconductor are connected to the surface of the side wall.
The optical module according to still another aspect of the present invention has an optical element and a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel. The P-type semiconductor and the N-type semiconductor have two ends. Moreover, there is a substrate provided with a first electrode that is disposed near the optical element, and second and third electrodes disposed at a distance from the optical element. A side surface of one end of the P-type semiconductor and the N-type semiconductor respectively is connected to the first electrode. A side surface of the other end of the P-type semiconductor is connected to the second electrode. A side surface of the other end of the N-type semiconductor is connected to the third electrode.
The optical module according to still another aspect of the present invention has a substrate and an optical element is mounted on the surface of this substrate. Moreover, there is a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel, the thermoelectric semiconductor having two ends. Moreover, there is a first conductor connected to one end surface of the P-type semiconductor and the N-type semiconductor respectively and the surface side of the substrate. There is a second conductor connected to the other end surface of the P-type semiconductor and the surface of the substrate. There is a third conductor connected to the other end surface of the N-type semiconductor and the surface side of the substrate.
The optical module according to still another aspect of the present invention has an optical element and a thermoelectric semiconductor that has a P-type semiconductor and an N-type semiconductor disposed in parallel. The P-type semiconductor and the N-type semiconductor have two ends. Moreover, there is a dielectric substrate that is connected to a side surface of one end and a side surface of the other end of the P-type semiconductor respectively, and to a side surface of one end and a side surface of the other end of the N-type semiconductor respectively. This dielectric substrate has a portion not in contact with the P-type semiconductor between the one end and the other end of the P-type semiconductor, and having a portion not in contact with the N-type semiconductor between the one end and the other end of the N-type semiconductor. Moreover, there is a substrate on which the optical element and the dielectric substrate are mounted.
The optical transceiver apparatus according to still another aspect of the present invention has an optical module and a circuit that provides a constant current to the thermoelectric semiconductor in the optical module to drive the thermoelectric semiconductor. This optical module is the optical module according to any one of the aspects according to the present invention described above.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed descriptions of the invention when read in conjunction with the accompanying drawings.